High temperature thermocouple



Sept. 15, 1931. H. c. STAEHLE 1,323,706

HIGH TEMPERATURE THERMOCOUPLE Filed Nov. 12. 1929 Inventor-Q Henry C. Staehle. WWW

His Attorney Patented Sept. 15, 1931 ,unrrso sTArss.

PATENT OFFICE mar c. srannm. or acetone, cononano; assmnoa 'ro GENERAL ELECTRIC commm, a conronamon or new aonx HIGH TEHPEBATUBE TEERMOCOUPLE This invention relates to a new and improved high temperature thermocouple.

Heretofore it has been difiicult to obtain a satisfactory high temperature thermocouple since few thermocouples are capable of withstanding for any length of time temperatures above 1600 C. n

I have discovered that I can obtain a satisfactory high temperature thermocouple which will have comparatively long life and uniform E. M. F. resistance at the high temperatures at which it is used, if I employ tantalum carbide and graphiteas the elements of the thermocouple. Because of its extreme infusibility tantalum carbide is capable of withstanding very high temperatures and in conjunction with 'aphite orms a thermocouple which can e ectively measure tem eratures ashigh as, and over, Q000 C. ince 2c tantalum carbide melts at over 4000 'C., and since graphite can withstand temperatures up to at least 2500 C., the range within which the thermocouple can operate is very great. Also tantalum carbide will not. recrystallize or become brittle at high temperatures.

Referring to the drawing accompanying andforming part of this applicatlo'mthe single figure there shown is a diagrammatic 3o cross-sectional view of an embodiment of my invention. a

In order to illustrate my invention I have shown in the figure ofthe drawing my new and improved thermocouple constructed in pencil type form. However, it will be obvious that the structure ma be modified without departing from the spirit or scope of the inventlon. The tube 1 is formed of graphite and is one element of the thermocouple. This 40 graphite tube receives at one end the tantalum carbide element which forms the other element of the thermocouple. This element may take the form of a wire 2, as shown. The end 3 constitutes the hot jungtion of the thermocouple. The tantalum carbide wire is spaced from the walls of the graphite tube and while it is in itself sufliciently rigid at the high ten}- peratures employed, it ma be held in place if desired by an insulating ug 4 which may be formed of any inert ins ating material, such as zirconia or thoria. Where the thermocouple is of a relatively small length the cold j u'nction thereof may be kept cool by means of several turns of copper tubing 5 suitably fixed to the graphite tube 1 through which tubing a coolin fluid such as water is circulated. Where t e length of the thermocouple Y is such that there is no danger of the cold end becoming heated this copper tubing arrangement may-be dispensed with. If it is used, however, contact may be made if-desired to" the graphite through the copper tubing as shown at 6, and contact with the tantalum carbide wire is made at 7. These contacts 6 and 7 may be connected by. means of suitable leads, 8 and 9, respectively, to'any suitable measuring instrument such as. "a millivolt meter or a potentiometer.

- A thermocouple of the t pe shownand described was found to deve op an E. M. F. of approximately 1 millivolt per 100 C. difference. A temperature of about 2000 C. 188 checked by an optical p rom'eter was recorded, although this is not t e maximum temperature at which the thermocouple of my inven tionmay be used. Atthis temperature the tantalum carbide was not afiected nor was there any indication of sag in the length used. What I claim as new and desire to secure by Letters Patent of the United States is:

A thermocouple the elements of which are tantalum carbide and graphite, respectively. In witness whereof, I have here nto set my hand this 5th da of November, 1929.

ENRY C. STAEHLE. 

